When I used to work for a boss, in an office cubicle, not so long ago, I used to commute to work. I took the subway and always carried a sketchbook with me to study and sketch the people around me. Waiting on the train platform or minding their own businesses in the carriage.
I don't miss that job. But sometimes I do miss the people-drawing-practice.

So, together with my sketch pal Yvonne, I went on an adventure to the Amsterdam Central Station and found a great spot on the first floor, right next to the monitors with the time tables for the departing trains. And drew this: